1. Field of the Invention
The present invention relates to an optical element having an integrated optical lens and lens holder, and to a production method for the optical element. More particularly, the present invention relates to a structure for holding an optical lens and a lens holder when press-molding the optical lens.
2. Description of the Related Art
In various fields of optical communication devices, optical information reading devices, and the like, optical elements in which an optical lens is held by a lens holder are used. In a well-known technique for producing such a conventional optical element, an optical lens is combined with the inner surface of a lens holder by press fitting when being press-molded from an optical glass material.
In the conventional optical element, a cylindrical or spherical lens material made of optical glass is placed in a lens holder made of metal, such as stainless steel, and generally shaped like a hollow cylinder; is heated and softened by a heating member; is pressed and deformed by being clamped by dies from above and below; and is press-fitted in the lens holder, whereby the lens material and the lens holder are combined. Moreover, lens optical surfaces are formed with an optical axis in the direction of the cylindrical axis of the lens holder by transferring the die surfaces onto the lens material.
As shown in FIGS. 3 and 4 however, in the above-described conventional optical element, gaps L1 and L2 of approximately 20 xcexcm are formed between the inner diameter of an inner wall 13a of a lens holder 13 into which a lens material 14 is press-fitted and the outer diameters of dies 11 and 12 for press-molding the lens material 14. Therefore, when the lens material 14 is press-molded, portions 14a and 14b of the deformed lens material 14 protrude in an annular ring outward through the gaps L1 and L2, and the shapes of outer peripheral edge surfaces 15c and 15d of lens optical surfaces 15a and 15b connected to the inner wall 13a of the lens holder 13 form a discontinuity and become disjointed and non-uniform.
For this reason, the protruding portions 14a and 14b of the lens material 14 formed at the outer peripheral edge surfaces 15c and 15d of the lens optical surfaces 15a an 15b may be broken and chipped due to vibration or external force, and glass powder formed thereby may adhere to the lens optical surfaces 15a and 15b. 
The present invention solves the above problems. An object of the present invention is to provide an optical element having an integrated optical lens and lens holder that prevents chipping and adhesion of glass powder resulting from protrusion of a part of an outer peripheral edge surface of a lens optical surface connected to the inner wall of the lens holder when a lens material is press-molded. It is another object of the present invention to provide a production method for the optical element.
In order to overcome the above problems, according to an aspect of the present invention, there is provided an optical element including a lens holder made of metal and shaped like a hollow cylinder, and an optical lens integrally held by an inner wall portion of the lens holder and having a lens optical surface at an opening in the direction of the optical axis, wherein an annular projecting portion is formed in the inner wall portion of the lens holder and adjacent to the opening, and an outer peripheral edge surface of the lens optical surface is placed under the projecting portion and is pressed in contact with the projecting portion over the entire periphery.
In this case, the shape of the outer peripheral edge surface of the lens optical surface connected to the inner wall portion of the lens holder is made continuous and uniform. This can prevent the lens optical surface from being broken and chipped due to vibration or external force and can prevent glass powder from adhering to the lens optical surface.
Preferably, a part of the projecting portion is buried in the outer peripheral edge surface of the lens optical surface. This allows the lens holder to reliably hold the optical lens.
According to another aspect of the present invention, there is provided an optical element production method including the steps of forming an annular projecting portion adjacent to an opening of an inner wall portion of a lens holder shaped like a hollow cylinder, inserting a lens material made of optical glass in the cylinder of the lens holder, press-fitting the lens material in the cylinder by heating, and pressing and deforming by a die, thereby forming a lens optical surface at the opening in the direction of the optical axis, and deforming the projecting portion by the die so that a part of the projecting portion is buried in an outer peripheral edge surface of the lens optical surface.
In this case, no gap is formed between the inner diameter of the inner wall portion of the lens holder and the outer diameter of the die when the lens material is press-molded, the deformed lens material does not partly protrude outward, and the shape of the outer peripheral edge surface of the lens optical surface connected to the inner wall portion of the lens holder can be made continuous and uniform.
According to a further aspect of the present invention, there is provided an optical element production method including the steps of inserting a lens material made of optical glass in a cylindrical portion of a lens holder shaped like a hollow cylinder, press-fitting the lens material in the cylindrical portion by heating, and pressing and deforming by a die, thereby forming a lens optical surface at an opening in the direction of the optical axis, extending a die surface for pressing a pressed surface of the lens material outside the inner wall of the cylindrical portion of the lens holder when pressing and deforming the lens material, and performing molding while an outer peripheral edge surface of the lens optical surface and an outer flat surface of the cylindrical portion of the lens holder are covered with the die surface.
In this case, no gap is formed between the inner wall of the lens holder and the die when the lens material is press-molded, the deformed lens material does not partly protrude outward, and the shape of the outer peripheral edge surface of the lens optical surface connected to the inner wall of the lens holder can be made continuous and uniform.
Further objects, features, and advantages of the present invention will become apparent from the following description of the preferred embodiments with reference to the attached drawings.